import numpy as np
import matplotlib.pyplot as plt
import math


def sigmoid(x):
    a = []
    for item in x:
        a.append(1.0 / (1.0 + math.exp(-item)))

    return a


x = np.arange(-10, 10, 0.1)
y = sigmoid(x)

plt.plot(x, y)
plt.show()
